Interpretive Summary: Quinoclamine is a new herbicide for the U.S. nursery market, currently under review at the US EPA. The herbicide is primarily being developed for postemergence liverwort control, although there is some speculation that the product may provide preventative (preemergence) liverwort control. The objective of this research was to document the amount of quinoclamine that is available for plant uptake in a pine bark substrate, then determine the amount of quinoclamine that is required for preventing liverwort germination from spores.
We found that typical application rates of quinoclamine result in sufficient concentration in a pine bark substrate to kill liverwort spores. We also documented that quinoclamine is actively absorbed by liverwort rhizoids (primitive roots) and translocated through the thallus (liverwort leaf) providing complete control.
This research provides additional information on the chemistry and behavior of quinoclamine in typical nursery substrates. Scientists can use this information to further understand how quinoclamine is sorbed to soils, absorbed by liverwort, and moved with liverwort plants. University extension agents can use the information to advise their clients on proper herbicide application timing and use.

Technical Abstract:
Quinoclamine is a herbicide under development for control of liverwort, a weed common in nursery crops. With respect to liverwort control, quinoclamine has been viewed as predominately postemergence active. However, some preemergence activity has been reported. Growth media sorption studies with 14C-quinoclamine indicates that only 0.64% of the quinoclamine amount that enters the media remains unabsorbed and thus available to be taken up by established plants and/or propagules. Computer modeling revealed that a large portion of the surface of the quinoclamine molecule is positively charged, which likely attributes to the observed high adsorptivity. In a simulation of preemergence activity, hydroponically-grown liverwort and germinating gemmae were exposed to increasing quinoclamine concentrations. Phytotoxicity to both plants and gemmae was obtained with a minimal concentration of approximately 4 to 6 mg L-1. Based upon the projected use rate, and assuming minimal vertical infiltration depth, the theoretical concentration within the aqueous phase of a pine bark substrate would be approximately 8 mg L-1. In toto, results indicate that the projected use rate will result in sufficient quinoclamine in the aqueous phase of a pine bark substrate to provide preemergence control of gemmae propagules as well as contribute to the efficacy of POST applications to established plant.